Carbide alloy

ABSTRACT

CARBIDE-METAL COMPOSITES OF SUPERIOR TOOL QUALITIES ARE PREPARED FROM SUBSTOICJHIOMETRIC CARBON-DEFICIENT MONOCARBIDE ALLOYS BASED ON TITANIUM, TUNGSTEN AND CARBON, AND BINDERS CONSISTING OF IRON METAL GROUP ALLOYS. THE IMPROVED TOOL QUALITIES ARE BASED IN PART ON THE DISCOVERY THAT SINGLE-PHASED MONOCARBIDE ALLOYS WITH SUBSTANTIALLY LARGER TUNGSTEN CONCENTRATIONS THAT IN THE COMMERCIALLY-USED, CARBON-SATURATED CARBIDES ARE POSSIBLE AT SUBSTOICHIOMETRIC COMPOSITIONS (5 TO 12 ATOMIC PERCENT CARBON DEFICIENCY). THE MICROSTRUCTURE IS CHARACTERIZED BY THE FINE MONOCARBIDE GRAINS EMBEDDED IN THE BINDER ALLOY MATRIX. A BENEFICIAL SMALL GRAIN SIZE IN SUBSTANTIALLY CARBON-DEFICIENT (8 TO 12 ATOMIC PERCENT) MONOCARBIDE ALLOYS IS OBTAINED BY IN SITU PRECIPITATION REACTIONS IN THE LARGER, PREMILLED CARBIDE GRAINS DURING FABRICATION.

June 5, 1973 U 3,737,289

CARBIDE ALLOY Filed July 29, 1970 3 Sheets-Sheet 1 7O 7O 5 "a Q- so 9 ATOMIC "/0 TUNGSTEN FIG. I

COMPOSITION TRIANGLE SHOWING CLAlMED COMPOSITION AREAS FOR Ti-W-C-BASED ALLOYS ERWIN RUDY, INVENTOR.

ATTORNEY June 5, 1973 Filed July 29, 1970 E. RUDY CARBIDE ALLOY 5 Sheets-Sheet 2 -0 CARBOLOY 350 A SUBSTOICHIOMETRIC Ti-W-C TOOL, I2% Ni FLANK WEAR, MILS CUTTING TIME, MINUTES FIG. 2

TIME-WEAR CURVES FOR NICKEL-BONDED, SUBSTOICHIOMETRIC Ti-W-C-BASED ALLOY IN COMPARISON TO CARBOLOY 350 ON HARDENED 4340 STEEL o CARBOLOY 370 III SUBSTOICHIOMETRIC Ti-W-C TOOL, I2/o Ni vii FLANK WEAR, MILS CUTTING TIME, MINUTES FIG. 3

TIME-WEAR CURVES FOR NICKEL-BONDED, SUBSTOICHIOMETRIC Ti-W-C-BASED ALLOY IN COMPARISON TO CARBOLOY 370 ON ANNEALED 4340 STEEL ERWIN RUDY, INVENTOR.

MQM

ATTORNEY June 5, 1973 E. RUDY 3,737,289

CARBIDE ALLOY Filed July 29, 1970 3 Sheets-Sheet 5 OCARBOLOY 37o ASUBSTOICHIOMETRIC Ti -w-c TOOL. |o% Co lo m 5 6 g o x Z f5 4 m CUTTING TIME, MINUTES TIME-WEAR CURVES FOR COBALT- BONDED SUBSTOICHIOMETRIC Ti-W-C BASED ALLOY lN COMPARISON TO CARBOLOY 370 ON ANNEALED 347 STAINLESS STEEL ERWl RUDY, INVENTOR.

BY M

ATTORNEY United States Patent 3,737,289 CARBIDE ALLOY Erwin Rudy, Beaverton, Oreg., assignor to Aerojet- General Corporation, El Monte, Calif. Filed July 29, 1970, Ser. No. 59,061 Int. Cl. B221? 3/12 US. Cl. 29-182.7 19 Claims ABSTRACT OF THE DISCLOSURE Carbide-metal composites of superior tool qualities are prepared from substoichiometric carbon-deficient monocarbide alloys based on titanium, tungsten and carbon, and binders consisting of iron metal group alloys. The improved tool qualities are based in part on the discovery that single-phased monocarbide alloys with substantially larger tungsten concentrations than in the commercially-used, carbon-saturated carbides are possible at substoichiometric compositions (5 to 12 atomic percent carbon deficiency). The microstructure is characterized by fine monocarbide grains embedded in the binder alloy matrix. A beneficial small grain size in substantially carbon-deficient (8 to 12 atomic percent) monocarbide alloys is obtained by in situ precipitation reactions in the larger, premilled carbide grains during fabrication.

DISCUSSION OF THE PRIOR ART Cemented carbides, including those commonly used as cutting tips for machining metal, are conventionally made by sintering a particulate mixture of tungsten carbide, titanium carbide and other refractory carbide additions, with cobalt or nickel. Cemented carbides are produced by milling or grinding together the carbide and cobalt and/or other iron group metals until they are intimately mixed as a fine powder, after which the powder is cold pressed to the desired shape, and the resulting porous but coherent body is then sintered in a reducing atmosphere or under vacuum to obtain dense bodies.

It is known that improved wear characteristics could be obtained by alloying tungsten monocarbide with other carbides of the refractory transition metals, for example, titanium. However, the solid solubilities of such other carbides in tungsten carbide are very small, with the result that when alloying is attempted, the carbide alloys appear in two phases, and for this reason the true potential of solid solution alloys has not been realized in the past A commercially-available high performance cutting tool material consists of a mixture of tungsten carbide and ternary cubic monocarbide solid solutions dispersed in a cobalt alloy matrix.

DESCRIPTION OF INVENTION It has been found that with carbon-deficient compositions, single-phased solid solutions of tungsten-titanium carbide containing substantially more tungsten than in the commercially-used, carbon-saturated alloys, can be prepared. In addition, a stability maximum has been observed in the carbon-deficient monocarbide near equiatomic metal concentrations. The monocarbide compositions of this invention are single-phased at high temperatures (Z000 C.); however certain monocarbide compositions undergo a disproportionation-precipitation reaction at temperatures used in sintering the carbide tool materials (1300 to 1500 C.). The amount of precipitate phase is dependent on the carbon defect and is not ice usually found in deficiencies smaller than 5 atomic percent; the precipitate from the disproportionation reaction is a tungsten-rich metal alloy formed in an oriented pattern Within the monocarbide grain. During sintering of the previously comminuted ingredients (carbide and binder metal), in the fabrication of the tool materials, these precipitates are dissolved into the larger quantity iron group metal to form the binder alloy. The ultimate effect of the precipitation-dissolu-tion reaction is a favor able reduction of the carbide grain size compared to the original grain size of the carbide obtained from the milling with some migration of tungsten occurring from the monocarbide alloy (by virtue of the precipitate-binder dissolution reaction) which, nevertheless, still contains substantially larger tungsten concentrations than in the commercially-used, carbon saturated carbides. Metal pre cipitation as a means for secondary grain size comminution becomes inoperative at carbon defects of less than 5 atomic percent. The benefit of smaller grain size derived from the precipitation-dissolution reaction as well as the advantage of larger tungsten concentration in the monocarbide is realized in the carbon-defect compositions of greater than 5 atomic percent. The high stability, substoichiometric monocarbide compositions, together with the added results of the precipitation-dissolution reaction, form the basis of the improved tooling materials hereinafter described.

The carbides of the invention comprise substoichiometric, carbon-deficient, single-phased monocarbide alloys of titanium, tungsten and carbon. The foregoing carbide alloys, embedded in a matrix of metals of the iron group, typically cobalt or nickel, find use in cutting tools and in other applications where abrasion resistance is required.

The disproportionation-dissolution reaction described above, while producing a tungsten-rich metal phase does not change the monocarbide from a single phase to two carbide phases, and, hence, the advantage over the prior art of the monocarbide being single-phased, and that phase deficient in carbon (and containing more tungsten in a single phase than the titanium carbide based commercial material) is retained along with the advantage of fine grain formation.

Other advantages of the invention will be apparent from the following detailed description and drawings in which:

FIG. 1 is a composition ternary showing desired composition areas for the Ti-W-C base alloys of the invention;

FIG. 2 is a graph presenting typical comparative wear curves obtained in turning 4340 steel with an embodiment of the tool of the invention and a commerciallyavailable tooling material (Carboloy 350);

FIG. 3 is a second graph obtained from results in turning 4340 steel with a tool of the invention and another commercially-available tooling material (Carboloy 370); and

FIG. 4 is a graph showing comparative wear data obtained in turning 347 stainless steel with a tool of the invention and a commercially-available cutting tool (Carboloy 370).

The carbide alloys of the invention can be prepared by direct combination of the elements (tungsten, titanium, other permissible alloy metals, and carbon), or by homogenizing pre-alloyed binary carbides at high temperatures, for example, 2000" to 2600" C., in a furnace, or

by are melting. For economic reasons the process of arc melting is usually preferable because it permits faster and more thoroughly homogenization of the monocarbide.

The reaction lumps of the carbide solid solution of the invention are subsequently crushed and ball milled to grain sizes typically less than 40 m. in preparing the master carbide alloy powder. The powders are analyzed for compositional consistency. The master carbide alloy powder, with or without additional alloying additions, is then mixed with the desired amount of iron group binder metal powder, typically 4 to 15 percent by weight of the mixture, and then ball milled for further comminution and thorough mixing. The powder mixture is then cold-compacted and sintered to full density using conventional powder metallurgy techniques.

The composition diagram of FIG. 1 depicts suitable base alloy compositions for producing the carbide component of the invention. The preferred compositions fall within the inner hatched area E,F,G,H. The larger area A,B,C,D of FIG. 1, more exactly, the area between inner area, E,F,G,H and the outer area A,B,C,D includes compositions of generally less suitable compositions for machine tool applications, but which are acceptable for other uses, for example, drawing dies or extrusion dies.

Melting and casting, plasma-arc spraying, as well as powder-metallurgical techniques have been employed in preparing the carbide compositions of the invention.

The carbide alloys of the invention may be extensively modified by alloying with other refractory carbides. The basic phase equilibrium characteristics of the Ti-W-C alloy system permit adapting the base composition to various needs by alloying; it is thus possible by alloying to tailor tool properties to specific requirements.

Tungsten in the base alloy compositions may be partially replaced by molybdenum up to about 17 atomic percent. Smaller quantities of chromium (up to about 3 atomic percent) may be substituted for tungsten. Hardness and oxidation resistance are increased by chromium additions, although at some sacrifice in strength. Vanadium, in concentrations up to 3 atomic percent, may be substituted for tungsten. The addition of molybdenum, and smaller amounts of vanadium, increases wettability between carbide and binder phase, without sacrifice of hardness and strength. Niobium and tantalum, in amounts up to about 15 atomic percent singly or in combination, may be substituted for tungsten or titanium, or both, without changing the basic phase equilibrium characteristics of the base alloy system. It has been found that zirconium in quantities up to 5 atomic percent, or hafnium in quantities up to 20 atomic percent, or combinations thereof not exceeding the individual limits, are essentially inert in respect to cutting behavior and may be substituted in part for the titanium. Other inert metals, such as for example Re, Mn, and rare earths, etc., in quantities up to about 2 atomic percent were shown to have no measurable effect on cutting performance.

The ternary monocarbide alloys of the invention typically have a gross carbon deficiency of 6 to 10 atomic percent, but nevertheless, the monocarbide remains single phased if prepared at temperatures about 2000 C.

Typical examples for the preparation of the compositions of the invention, including the preparation of the ingredient alloys and the fabrication of tool materials therefrom, are given below:

EXAMPLE I A carbide alloy with the gross composition Ti-Ta-W-C (29-3-24-44 atomic percent) was prepared by hot pressing a mixture of the powdered ingredients TiC, WC, Ta, and W in graphite dies. The hot pressed body was homogenized for 25 hours at 1640 C. under a vacuum of approximately 10 torr. The carbide was then broken up, crushed, and ground to a grain size less than 105 m. under a helium atmosphere. After addition of 12 weight percent nickel powder to the carbide, the mixture of carbide alloy and binder phase was then ball milled for 72 hours under acetone. The slurry was then filtered and the powder cake dried under helium. The grain size attained was in the order of 2 to 10 m. A camphor-in-ether solution was then admixed to the powder to serve as a pressing aid, the ether allowed to evaporate, and the mixture compacted at a pressure of about 4 tons per cm. The camphor was driven off under vacuum at temperatures between 50 and C., and the green compacts then presintered for 30 minutes at 1300" C. under a vacuum of 10 torr. The compacts, which in the presintered state were still quite porous but had sufficient strength to be handled without danger of breakage, were then cut into tool bit-sized shapes and sintered to full density at 1450 C. (2% hours) under vacuum. The macrohardness (Rockwell A hardness) of the dense tooling material Was R =91, and the microscopic examination revealed equiaxed carbide grains em bedded in the nickel binder matrix.

The raw tool bits were then brazed onto mild steel tool holders and ground with diamond wheels to the desired tool shape. The tool geometry for the evaluation of the tools in straight turning tests on 4340 steel was as follows: back rake, 5 side rake, 5 side relief, 5; end relief, 5; SCEA, 25; ECEA, 25.

The tests were carried out on a Le Blonde machinability lathe, using applicable commercial tooling materials (Carboloy), as quality comparison standards.

Test 1 Test material: 4340 steel, annealed, vacuum degassed, and

heat-treated to R =46. Test conditions:

Cutting speed: 200 s.f.m. (surface feet per minute) Depth of cut: .050 inch Feed: .010 inch/rev. Lubricant: PEM 202 cutting fluid Comparison tool: Carboloy 350 (C-7 grade) After 40 minutes cutting time, total flank wear on the substoichiometric tool of the invention was 8 mils, as compared to 13 mils for the Carboloy 350 tool. The significant feature of the time-wear characteristics, as shown in FIG. 2, concerns the observation that after the wear-in period of about 20 minutes, the wear rates on the substoichiometric tool approached stationary values considerably below those of the comparison tool. Extrapolation of the flank wear to the standard endpoint of .016 inch yields therefore an unproportionately longer tool life for the substoichiometric alloy than would be indicated by a direct comparison of the cumulative flank wear after a fixed time period.

Test 2 Test material:

4340 steel, annealed and vacuum degassed.

Condition C, BHN 223. Test conditions:

Cutting speed: 500 s.f.m.

Depth of cut: .050 inch Feed: .010 inch/rev.

Lubricant: PEM 202 cutting fluid Comparison tool: Carboloy 370 (C-5 grade) After a cutting time of 20 minutes, as shown in FIG. 3, total flank wear on the substoichiometric tool was 11 mils, whereas the comparison tool had reached the end of its practical tool life (.016 inch).

EXAMPLE II An alloy with the gross composition Ti-W-C (33-25-42 atomic percent) was prepared by hot pressing a mixture of TiC, WC, and W. Coarse crushings of the compact were then melted in a non-consumable electrode (W) are furnace, the melted buttons again crushed and ball-milled to a grain size less than 50 m. After addition of 10 weight percent cobalt, ball milling was continued for 72 hours under acetone. Further processingof the powders and compacts were the same as described in Example I.

Microscopic inspection showed the gross structure to be similar to the cutting tool described in Example I, except for a pronounced substructure within the carbide grains. Closer examination revealed this substructure to consist of a continuous metal sub-lattice formed by precipitation and subsequent reactions of the precipitated metal phase with the liquid cobalt alloy at sintering temperatures. The effective grain size of the carbide thus appeared to have been reduced to about 3 m.

Straight turning tests were again used to determine tool performance. The tool geometry was as follows: back rake, side rake, 5; side relief, 5; end relief, 5'; SCEA, 25 ECEA, 25.

Machinability test Test material: AISI 347 stainless steel, BHN 223 Cutting speed: 400 s.f.rn.

Depth of cut: .050 inch Feed: .010 inch/rev.

Lubrication: None Comparison tool: Carboloy 370 (06 grade) After cutting time of 40 minutes (FIG. 4) the substoichiometric carbide tool had a flank wear of 6% mils, as compared to about 9 mils of the Carboloy 370 tool.

The preparation and evaluation of test samples containing other alloying additions including vanadium, niobium, chromium, zirconium and hafnium were analogous to those described in the above examples.

I claim:

1. Carbide alloy comprising a substoichiometric, carbon-deficient, single-phased monocarbide based on titanium, tungsten and carbon wherein the composition of the titanium-tungsten-carbon alloy is selected from within the area A, B, C, D of the composition diagram of FIG.

2. Carbide alloy in accordance with claim 1 wherein the composition of the titanium-tungsten-carbon alloy is selected from the more limited area of E, F, G, H of the composition diagram of FIG. 1.

3. A carbide-metal composite comprising carbide grains embedded in a binder matrix of a metal of the iron group, or their alloys, said grains comprising a substoichiometric, carbon-deficient, single phased monocarbide based on titanium, tungsten and carbon, wherein the titanium-tungsten-carbon base alloy is selected from the area A, B, C, D of the composition digram of FIG. 1.

4. A carbide composite in accordance with claim 3 wherein the titanium-tungsten-carbon base alloy is selected from the more limited area E, F, G, H of the composition diagram of FIG. 1.

5. The metal-carbide composite comprising carbide grains embedded in a binder matrix of nickel in an amount of 12 percent based on the weight of composite, said carbide grains comprising a substoichiometric, carhon-deficient, single-phase monocarbide of titanium, tantalum, tungsten and carbon, wherein these constituents are present in the ratio of the following atomic percentages:

6. The metal-carbide composite comprising carbide grains embedded in a binder matrix of cobalt in an amount of percent based on the weight of composite, said carbide grains comprising a substoichiometric, carbon-deficient, single-phased monocarbide of titanium, tungsten and carbon, wherein these constituents are present in the ratio of the following atomic percentages:

7. The carbide-metal composite of claim 3 wherein the matrix metal consists of 4 to 15 percent by weight based on the composite.

8. A carbide alloy whose microstructure consists of a fine grained, substoichiometric, carbon-deficient, single phased, monocarbide; the composition of said monocarbide comprising:

from about 25 to about 48 atomic percent titanium;

from about 7 to about 37 atomic percent tungsten;

from about 38 to about 45 atomic percent carbon; the sum of the constituents totalling atomic percent, and wherein all of the constituents of the alloy are of normal commercial purity.

9. A carbide alloy as in claim 8 wherein the titanium content is from about 29 to about 36 atomic percent, and the tungsten content is from about 19 to about 33 atomic percent.

10. A carbide-metal alloy composite comprising the alloy of claim 8, said alloy embedded in a metal matrix of iron, cobalt, nickel or any combination thereof. 7

11. A carbide-metal alloy composite comprising the alloy of claim 9, said alloy embedded in a metal matrix of iron, cobalt, nickel, or any combination thereof.

12. A carbide-metal alloy composite as in claim 10 wherein said metal matrix comprises from about 4 to about 15 weight percent of said composite.

13. A carbide-metal alloy composite as in claim 11 wherein the metal matrix comprises from about 4 to about 15 weight perecnt of said composite.

14. A carbide alloy whose microstructure consists of a fine grained, substoichiometric, carbon-deficient, single phased, monocarbide; the composition of said monocarbide comprising:

(A) titanium and alloying substituents consisting essentially of hafnium, niobium, tantalum and zirconium in the range of about 25 to about 48 atomic percent wherein:

titaniuminiobiumitantalum are present from about 0 to about 15 atomic percent;

titaniumizirconium are present from about 0 to about 5 atomic percent;

titaniurnihafnium are present from about 0 to about 20 atomic percent;

the balance, if any, being titanium;

(B) tungsten and alloying substituents, consisting essentially of chromium, molybdenum, vanadium, tantalum and niobium in the range of about 7 to about 37 atomic percent wherein:

tungstenichromium are present from about 0 to about 3 atomic percent;

tungsten: molybdenum are present from about 0 to about 17 atomic percent;

tungstenivanadium are present from about 0 to about 3 atomic percent;

tungstenitantaluminiobium are present from about 0 to about 15 atomic percent;

the balance, if any, being tungsten;

(C) carbon from about 38 to about 45 atomic percent;

the atomic percentages of niobium and tantalum, each alone or in combination, never exceeding 15 atomic percent;

the total atomic percentage of all constituents being 100 atomic percent, wherein all of the constituents of the alloy are of normal commercial purity;

the terms (1+) denoting a metal is present, and denoting a metal is absent from the alloy.

15. A carbide alloy as in claim 14 wherein the total atomic percentage of titanium and the said alloying substituents is in the range of 29 to 36 atomic percent; the total atomic percentage of tungsten and the said alloying substituents is in the range of 19 to 33 atomic percent.

16. A carbide-metal alloy composite comprising the alloy of claim 14, said alloy embedded in a metal matrix of iron, cobalt, nickel, or any combination thereof.

17. A carbide-metal alloy composite comprising the alloy of claim 15, said alloy embedded in a metal matrix of iron, cobalt, nickel or any combination thereof.

18. A carbide-metal alloy composite as in claim 16 wherein said matrix comprises from about 4 to about 15 weight percent of said composite.

19. A carbide-metal alloy composite as in claim 17 wherein said matrix comprises from about 4 to about 15 weight percent of said composite.

8 References Cited Chemical Abstracts, vol. 67, p. 5341, Abstract 566389, Amer. Chem. Soc.

LELAND A. SEBASTIAN, Primary Examiner B. HUNT, Assistant Examiner US. Cl. X.R. 29182.8; 75203, 204 

